The present invention relates to mine roof bolt anchoring and, more specifically, to improved apparatus for use in a combined mechanical-resin bolt anchoring system.
In copending U.S. application Ser. No. 882,797 of Carl A. Clark and John Rogalla, assigned to applicant's assignee, is disclosed bolt anchoring apparatus and methods which involve common rotation of the bolt and an associated expansion anchor to break a two-compartment resin package and mix the contents thereof. Cooperating structure on, or in association with, the bolt and anchor cause the two to be rotated together, i.e., relative rotation is prevented, when the bolt is turned in a counter-clockwise direction. The cooperating structure allows relative rotation in the opposite direction, however, whereby the anchor may be held stationary as the bolt is rotated in the clockwise direction to advance into the tapered nut and effect expansion of the anchor. The advantages of such a system are discussed more fully in the aforementioned application, as are the various prior art systems.
In practise, it has been found that at least some forms of the apparatus described in the aforementioned application encounter excessive friction between the bolt and anchor as the bolt is rotated in the clockwise direction. Therefore, instead of the anchor remaining rotationally stationary to permit advancement of the bolt into the tapered nut to cause expansion of the shell, it is rotated with the bolt as in the counter-clockwise direction. Thus, in some cases the shell does not expand and the bolt is not tensioned as desired.
It is the principal object of the present invention to provide an improved construction for transmitting rotation from a roof bolt to an expansion anchor in one direction while allowing relative rotation in the opposite direction.
Another object is to provide a resilient coupling for use with a mine roof bolt and associated expansion anchor which effectively transmits rotation from the bolt to the anchor in one direction while allowing relative rotation by offering very little frictional resistance in the opposite direction to insure expansion of the anchor.
Other objects will in part be obvious and will in part appear hereinafter.